Microlithography is a widely used industrial process which is employed for the production of surface relief images having extremely small pattern elements. Microlithography is used for example by the electronics industry in the manufacture of large scale integrated circuits which can have circuit elements which are in the submicron to a few micron size range.
In microlithography a film of material known as a resist is exposed with a high energy source. The resists which are generally employed are polymeric materials which, when exposed to a high energy source, are altered in their solubility to become either more soluble or less soluble in selected solvents. By exposing the resist in preselected areas and thereafter treating the exposed resist with a solvent, the more soluble areas after exposure can be selectively removed to provide a surface relief pattern in the resist. The surface relief pattern is then used in further processing steps to produce the desired final product.
Various high energy sources can be used to expose resists. These sources include for example visible light, ultraviolet radiation, and an electron beam. Each of the forms of energy which are currently employed for exposing resists have certain inherent problems. Ultraviolet exposure apparatus has a relatively low initial cost and low operating cost. However, with ultraviolet radiation exposure, and especially with visible light exposures, there is a limitation on the resolution capability and the size of the patterns which can be produced because of the relatively long wavelengths of these forms of energy. Electron beam radiation can be used to produce relief images having substantially smaller pattern elements and having a high degree of resolution. Electron beam lithography, however, must be conducted with apparatus which has an extremely high initial capital cost and further has a very high cost of operation. A typical apparatus which is suitable for electron beam exposures in which resists are exposed to produce surface relief patterns which have extremely small pattern elements and a high degree of resolution is described in U.S. Pat. No. 3,909,737 issued to R. J. Collier.
The high initial cost and high operating costs of suitable electron beam exposure systems have made them impractical for laboratory scale evaluations and for the commercial manufacture of circuits and the like which are produced in relatively low volumes or sold at a low cost per unit.
Accordingly, it would be highly advantageous if apparatus could be provided having the fine geometry capabilities and the high resolving properties of the electron beam exposure systems now employed, but which would have both a lower initial capital cost and lower operating costs on the level of conventional ultraviolet exposure apparatus so as to be feasible for both laboratory scale experiments and evaluations and for commercial production of limited numbers of parts.